Elongated element comprising helically patterned adhesive

ABSTRACT

A threadlike or ribbonlike elastic strand is provided with a substantially continuous filament of adhesive helically wrapped around the elastic strand. The elastic strand is suitable for use in disposable absorbent products such as diapers and adult incontinent products. Also disclosed is a method and apparatus for making such adhesive-wrapped elastic strands.

This is a continuation of copending application(s) Ser. No. 07/689,230filed on Apr. 22, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to adhesive-wrapped elongated elements,such as threadlike or ribbonlike strands of elastic. Specifically, thepresent invention relates to adhesive-wrapped elongated elements whereinthe adhesive forms a substantially continuous helical pattern.

2. Background of the Related Art

The use of elongated elements, such as threadlike or ribbonlike strandsof elastic in the manufacture of disposable absorbent products, such asdiapers, adult incontinence products, feminine care products, trainingpants, and the like, is known. In the case of diapers and adultincontinence products, the elastic strands generally are located aroundthe waist of the garment and/or at the leg openings.

Disposable absorbent products, such as diapers, adult incontinenceproducts, and the like, generally comprise an outer cover, awater-pervious inner liner, and an absorbent structure located betweenthe outer cover and inner liner. When elastic strands are employed inthe manufacture of such disposable garments, the elastic strands aregenerally adhered to either the outer cover, the inner liner, or boththe outer cover and inner liner. A variety of methods have been proposedfor adhering the elastic strands to a substrate, such as the outer coveror inner liner.

For example, U.S. Pat. No. 4,666,542 issued May 19, 1987, to DeJonckheere is directed to a process for the production of disposablediaper panties. The disclosed process starts with a multistrand elastictape which is separated into two arrays of four individual elasticstrands. Each individual strand is passed through a longitudinal grooveof an adhesive application unit. The strands are said to be completelycoated with a hot-melt liquid adhesive. The strands are then broughtinto contact with, and adhesively bonded to, a flexible sheet.

Coating the entire surface of the elastic strand employs a relativelylarge amount of the hot-melt adhesive. For economic reasons, this isoften undesirable.

U.S. Pat. No. 4,842,666 issued June 27, 1989, to Werenicz is directed toa process for the permanent joining of stretchable threadlike or smallribbonlike elastic elements to a flat substrate, as well as use thereoffor producing frilled sections of film or foil strip. Disclosed is aprocess for joining elastic elements to a flat substrate by means of anadhesive. The process is characterized in that one disposes, or fixes,in the desired position, one or several elastic elements on a flatsubstrate, or guides them in the desired position at a distance of fromabout 0.1 to about 3 centimeters from the flat substrate. The elasticelements and some portion of the adjacent region of the substrate arethen covered with a sprayed-on melt adhesive. In the case of guiding ata distance, the elastic elements are then brought into contact with thesubstrate.

Again, spraying an adhesive on the elastic elements, as well as onadjacent areas of the substrate, employs a relatively large amount ofadhesive. Due to the cost of such adhesive, this is not alwaysdesirable. Additionally, the elastic strands are often applied to thesubstrate in a stretched condition so that, when relaxed, the elasticstrands contract and form rugosities in the substrate. Application ofadhesive to the substrate in an area adjacent the elastic strands mayinterfere with the formation of the rugosities. Specifically, since theadhesive may be less flexible than the substrate, the presence of theadhesive may reduce the flexibility of the substrate, thereby reducingthe ability of the elastic elements to contract the substrate.

U.S. Pat. No. 4,880,420 issued Nov. 014, 1989, to Pomparelli is directedto multiple strand elastic means. Disclosed are elastic means comprisingsubstantially parallel multiple strands of stretched elastic adheredbetween two layers of a fabric by at least one sinusoidal adhesive line.The use of the sinusoidal adhesive line is said to hold the elasticstrand sufficiently in place while using a minimum amount of adhesive.The sinusoidal line of adhesive is described as being applied to thesubstrate to which the elastic material is to be adhered.

When the adhesive is applied to the substrate, the adhesive almostalways covers a portion of the substrate adjacent to the elasticstrands. As discussed above, this can interfere with the ability of theelastic strands to gather the substrate. Accordingly, in some instances,it is more desirable to apply the adhesive to the elastic strand ratherthan to the substrate to which the elastic strand is to be applied. Foreconomic reasons, it is almost always desirable to use the minimumamount of adhesive necessary to achieve the desired results.

It is desirable to provide a method for adhering elongated elements suchas elastic strands to a substrate, which method involves the use of theminimum amount of adhesive necessary to obtain the desired degree ofadhesion, and which method involves adhesive contacting the substratewhere necessary to adhere the elongated element to the substrate. It isthis and to related goals to which the present invention is directed.

SUMMARY OF THE INVENTION

The present invention provides an elongated element having asubstantially continuous filament of adhesive helically wrapped thereon.The helically wrapped adhesive has been found to provide sufficientadhesive to adhere the elongated element to a substrate and yet has beenfound to require a relatively small amount of adhesive compared to othermethods known in the art. Additionally, the helically wrapped adhesivehas been found capable of adhering the elongated element to a substratewithout coating adjacent areas of the substrate with large amounts ofthe adhesive. Also disclosed is a process and apparatus for forming theadhesive-wrapped elongated element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an adhesive-wrapped elongated elementaccording to the present invention.

FIG. 2 illustrates the process of forming the adhesive-wrapped elongatedelement illustrated in FIG. 1.

FIG. 3 illustrates an adhesive-wrapped elastic strand, according to thepresent invention, adhered to a substrate while the elastic strand is ina stretched condition.

FIG. 4 illustrates an adhesive-coated elastic strand illustrated in FIG.3 while the elastic strand is in a relaxed condition.

FIG. 5 illustrates the apparatus for forming the adhesive-wrappedelongated elements of the present invention.

FIG. 6 illustrates adhesive-wrapped elastic strands, according to thepresent invention, in place to form the leg elastics of a disposablediaper.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be described inconnection with elongated elements which comprise threadlike orribbonlike elastic strands suitable for use as the leg elastics or waistelastics of a disposable infant or adult diaper. It is to be understoodthat the present invention is equally applicable to any elongatedelement whether or not such element is elastic in nature. Additionally,while the preferred embodiments will be described in connection withinfant or adult diapers, it is to be understood that the adhesive-coatedelongated elements can be joined to a variety of substrates suitable formany divergent uses.

The present invention can best be illustrated by reference to theaccompanying drawings wherein FIG. 1 illustrates an adhesive-wrappedelastic strand 10. The adhesive-wrapped elastic strand comprises athreadlike elastic strand 12 having a substantially continuous filamentof adhesive 14 helically wrapped thereon.

The "pitch" of the helix is best described by referring to the number ofrevolutions the helix makes around the elastic strand over a given unitof length. In the drawings, one revolution is illustrated as occurringover the distance R. The helically wrapped adhesive will generally makefrom about 0.5 to about 100, preferably, from about 2 to about 25revolutions per inch of the elastic strand. The number of revolutionsper inch the helix of adhesive makes around the elastic strand may beregular along the length of the elastic strand or may vary along thelength of the strand. For example, the helix of adhesive may make 5revolutions per inch for some length of elastic strand and may then make15 revolutions per inch for some length of elastic strand.

For the purposes of this application, the number of revolutions thehelix of adhesive makes per inch will be determined at the time theelastic strand is brought into contact with the substrate to which it isto be adhered. Thus, if the elastic strand is in a stretched conditionwhen adhered to a substrate, the number of revolutions per inch will bedetermined while the elastic strand is in a stretched condition.

Elastic strands suitable for use in the present invention are known tothose skilled in the art. Typically, the elastic strands are eitherthreadlike or ribbonlike in shape. The elastic strands can have across-sectional area of from about 0.005 square millimeter to about 2.00square millimeters, preferably from about 0.01 square millimeter toabout 1.0 square millimeter, and most preferably from about 0.01 squaremillimeter to about 0.6 square millimeter. Exemplary of the elasticmaterials suitable for use in the present invention are a urethane film,commercially available from Deerfield Urethane Company under the tradedesignation Tuftane™, and Spandex urethane strands commerciallyavailable from Dupont Chemical Company, under the trade designationLycra-XA™. The urethane strands suitably have a cross-sectional area ofabout 0.2 square millimeters.

A wide variety of adhesives are also suitable for use in the presentinvention. The exact adhesive chosen will depend to a large extent onthe nature of the elastic strand to be adhered, the use to which theelastic strand is to be put, and the environment in which the elasticstrand is to operate. When the elastic strands are to be employed indisposable diapers, the adhesive is suitably a hot-melt adhesive such asthat commercially available from the Findley Adhesive Company under thetrade designation Findley H2096.

FIG. 2 illustrates a process according to the present invention.According to the process illustrated in FIG. 2, a substantiallycontinuous filament of adhesive 14 is extruded from orifice 16. Thefilament of adhesive 14 is then brought into contact with the elasticstrand 12 such that the adhesive wraps around the elastic strand in asubstantially continuous helical pattern. In the illustratedembodiments, the helical wrapping of the adhesive filament 14 around theelastic strand 12 is caused by rotating the elastic strand about itscentral longitudinal axis while the elastic strand 12 is moving pastorifice 16 in direction D. The number of revolutions the filament ofadhesive 14 makes per inch of elastic strand 12 is dependent on thespeed at which the elastic strand 12 moves past orifice 16 and on thespeed at which the elastic strand 12 is rotated about its centrallongitudinal axis.

Methods of extruding a substantially continuous filament of adhesivefrom an orifice are known to those skilled in the art. When the adhesiveis a hot-melt adhesive, the orifice 16 is suitably part of a hot-meltadhesive nozzle such as that commercially available from NordsonCorporation.

The adhesive 14 desirably has a high enough viscosity to form asubstantially continuous filament when extruded from orifice 16.Applicants have found that, once such filaments of adhesive contact theelastic strand 12, they tend to adhere thereto until such time as thefilament of adhesive becomes discontinuous. It is anticipated that therewill be occasional breaks in the continuity of the adhesive filament 14.A filament will be considered to be substantially continuous as long asany discontinuity is not so great as to degrade the performance of theadhesive to an unacceptable level. Typically, the adhesive will becontinuous over a length of at least about 1 inch, preferably of atleast about 2 inches, more preferably of at least about 5 inches andmost preferably over the entire length of the strand.

The adhesive-wrapped elastic strand is then brought into contact withthe substrate to which the elastic strand is to be adhered. In the caseof a hot-melt adhesive, the elastic strand must be brought into contactwith the substrate while the adhesive is at a temperature above its setpoint. FIG. 3 illustrates the adhesively wrapped elastic strand of FIG.1 in place on a substrate 18. The elastic strand 12 is adhered tosubstrate 18 by the adhesive filament 14 at adhesion points 20. Thenumber of adhesion points 20 along a given length of elastic strand 12is dependent on the number of revolutions which the adhesive filament 14makes per inch of elastic strand 12. The elastic strand 12 isillustrated in a stretched condition in FIG. 3.

In order to minimize the amount of adhesive employed in adhering theelastic strand 12 to substrate 18, it is desired that the number ofadhesion points 20 per given length of elastic strand be the minimumnumber necessary to adhere the elastic strand 12 to substrate 18 withsufficient force for a given use. Thus, when the elastic strand 12 isemployed in a disposable garment such as a diaper, it is desired thatthere be the minimum number of adhesion points 20 present to allow theelastic strands to, for example, form the leg elastics of the diaper.The minimum number of adhesion points 20 for a particular use is easilydetermined by experimentation. To the extent more revolutions ofadhesive are present than are required, excess adhesive is beingutilized.

FIG. 4 illustrates the elastic strand 12 adhered to substrate 18,illustrated in FIG. 3, when said elastic strand 12 is in a relaxedcondition. From FIG. 4 it is seen that elastic strand 12 causes thesubstrate to be gathered to form a series of ruffles. A ruffle will beformed in the substrate 18 between the adhesion points 20. Thus, bycontrolling the number of adhesion points 20, one can control the numberof ruffles or gathers formed in a given length of the substrate.Specifically, when a relatively low number of adhesion points 20 occurover a given length of substrate 18, the gathers formed will berelatively small in number and relatively large in size. Conversely,when there are a relatively large number of adhesion points 20 over agiven length of substrate 18, the ruffles or gathers formed will berelatively large in number and will be relatively small in size.

From reference to FIGS. 3 and 4, it is seen that the adhesive contactssubstrate 18 only at adhesion points 20. Little, if any, adhesive ispresent on the substrate adjacent the elastic strand 12. Applicants havefound that this is desirable, since the presence of excessive adhesiveis economically inefficient and may inhibit the gathering or ruffling ofsubstrate 18.

The adhesive-wrapped elastic strand 12 can also be used to join twosubstrates together and to elastically constrict both substrates. Thisaspect of the invention will be further illustrated in connection withFIG. 5, wherein an apparatus suitable for joining an elastic strand to asubstrate with an adhesive is illustrated.

FIG. 5 illustrates extrusion means 22 and orifice 16 for providing asubstantially continuous filament of adhesive 14. The substantiallycontinuous filament of adhesive 14 is brought into contact with elasticstrand 12 supplied from supply means 24. Supply means 24 suitablycomprises a supply roll and is positioned with respect to extrusionmeans 22 and orifice 16 such that the substantially continuous filamentof adhesive 14 is brought into contact with elastic strand 12. Theelastic strand 12 is caused to rotate about its central longitudinalaxis by means 26. The rotation of elastic strand 12 about itslongitudinal axis causes the adhesive filament 14 to wrap around theelastic strand in a substantially continuous helical pattern. Means forrotating the elastic element about its central longitudinal axis areknown to those skilled in the art. In the illustrated embodiment, means26 comprises a nip roll assembly rotating at an angle to the elasticstrand 12. Additionally, it is believed possible to cause the elasticstrand 12 to rotate about a central axis by wrapping elastic strand 12on supply means 24 in such a manner that, as elastic strand 12 isunrolled from supply means 24, it rotates in a direction opposite thatof which it was rotated when wrapped on supply means 24.

Substrate 18 is provided from supply roll 28 and is brought into contactwith the adhesive-wrapped elastic strand at point 30. As discussedabove, a second substrate 32 can also be brought into contact with theadhesive-wrapped elastic strand such that the elastic strand is adheredto both substrates 18 and 32. Suitably, the elastic strand andsubstrates 18, 32 are passed through nip rollers 34 to compress thesubstrates against the adhesive-wrapped elastic strand.

Almost any substrate is suitable for use in the present invention. Whenthe elastic strands are intended for use to gather or ruffle asubstrate, the substrate must be sufficiently flexible, relative to thecontractile strength of the elastic strand, to allow the strand tocontract the substrate. As a general rule, the substrates are clothlikeand relatively easily gathered. When the adhesive-wrapped elasticstrands are intended for use in disposable diapers, the substrate isgenerally a flexible, clothlike component of the diaper.

With reference to FIG. 6, a disposable diaper 36 is illustrated.Disposable diaper 36 comprises a water-pervious inner liner 38, an outercover 40, and an absorbent structure 42 located between the superposedouter cover 40 and inner liner 38. In the illustrated embodiment, theadhesive-wrapped elastic strands 10 are positioned to form gaskets aboutthe leg of a wearer. The adhesive-wrapped elastic strands are adhered toboth the inner liner 38 and the outer cover 40. In this manner, theelastic strands 12 will serve to contract both the outer cover and theinner liner. Exemplary disposable diapers are generally described inU.S. Pat. Nos. 4,710,187 issued Dec.1, 1987 to Boland et al.; 4,762,521issued Aug. 9, 1988, to Roessler et al.; 4,770,656 issued Sep. 13, 1988,to Proxmire et al.; and 4,798,603 issued Jan. 17, 1989 to Meyer et al.,which references are incorporated herein by reference.

Those skilled in the art will recognize that the present invention iscapable of many modifications and variations without departing from thespirit of the invention. Accordingly, the detailed descriptions of thepreferred embodiments set forth above are meant to be illustrative onlyand are not meant to limit the scope of the following claims.

What is claimed is:
 1. An adhesive-wrapped elastic element, said elementcomprising an elastic strand having a substantially continuous filamentof adhesive helically wrapped thereon and adhesively adhered thereto. 2.The adhesive-wrapped elastic element according to claim 1 wherein theadhesive is a hot-melt adhesive.
 3. The adhesive-wrapped elastic elementaccording to claim 2, wherein the helix of adhesive forms from about 0.5to about 100 revolutions per inch of elastic strand.
 4. Theadhesive-wrapped elastic element according to claim 3 wherein the helixof adhesive forms from about 2 to about 25 revolutions per inch ofelongated element.
 5. An adhesive-wrapped elastic element, said elementcomprising a threadlike or ribbonlike elastic strand formed of aurethane material and having a cross-sectional area of from about 0.005to about 2.0 square millimeters, said elastic strand further having asubstantially continuous filament of adhesive helically wrapped thereonand adhesively adhered thereto.
 6. The adhesive-wrapped elastic elementaccording to claim 5 wherein the helix of adhesive forms from about 0.5to about 100 revolutions per inch of elastic strand.